Conventionally, a rubber stopper for collectively protecting multiple electric wires from water disclosed in JPH11-329567A (Patent Document 1) has been known. The rubber stopper includes multiple wire through holes through which the electric wires are passed, respectively. Outer peripheries of the electric wires are tightly held against inner walls of the respective through holes to tightly fit the electric wires in the rubber stopper. Furthermore, an outer periphery of the rubber stopper is tightly held against an inner wall of a rubber stopper attachment hole of a case to tightly fit the rubber stopper in the case.